A negative glow lamp typically is comprised of a light transmitting envelope containing a noble gas and mercury with a phosphor coating on an inner surface of the envelope which is adapted to emit visible light upon absorption of ultraviolet radiation that occurs when the lamp is excited. The lamp is excited by means of the application of a voltage between the lamp electrodes. Current flows between the electrodes after a certain potential is applied to the electrodes, commonly referred to as the breakdown voltage. An elementary explanation of the phenomenon is that the gas between the electrodes becomes ionized at a certain voltage, conducts current, and emits ultraviolet radiation. Examples of typical glow discharge lamps are found in U.S. Pat. No. 2,067,129 to Marden; U.S. Pat. No. 3,814,971 to Bhattacharya; and U.S. Pat. No. 4,408,141 to Byszewski et al.
As stated, the instant invention pertains to negative glow discharge lamps of the variety described above. The invention defines a glow lamp which contains a predetermined amount of an impurity (i.e., nitrogen) in the fill gas which results in an improved lamp efficacy (i.e., light output per lamp wattage).
In the past, nitrogen has been introduced into conventional fluorescent arc discharge lamps with limited success. One such lamp is described in U.S. Pat. No. 2,419,902, which issued to Mager on Apr. 29, 1947. This patent teaches the introduction into the lamp gas fill of an amount of nitrogen which is from 0.3 percent to 1.5 percent. It also teaches that quantities larger than 1 percent do not increase the efficiency greatly and do make the lamps much harder to start initially. The nitrogen improves the lumen maintenance of the lamp by 10 percent.
In a preprint of a paper presented at the National Technical Conference of the Illuminating Engineering Society in September of 1956 entitled "Fluorescent Lamp Performance as Affected by Impurity Gases", Mooney et al teach that small concentrations of nitrogen (i.e., 0.1 percent) introduced into an argon-filled F20T12 fluorescent lamp seem to be advantageous to lumen maintenance. However, a concentration of 1 percent nitrogen is shown in FIG. 2 of the reference to result in a decrease in efficiency beginning at about 750 hours. Mooney et al, like Mager, also point out that nitrogen may result in difficulties in lamp starting.
In a paper entitled "A study of the Effects of Gas Impurities in Fluorescent Lamps" which was contributed to the Symposium on Electronics, 1945, Kenty et al teach that nitrogen admitted at an end of the lamp at a constant rate of 5.7 L.mu./hr causes a brownish-yellow deposit which is unstable under the discharge and tends to draw together into patches.